This disclosure relates to an improved on-line color measurement and control system for color printers, especially, for providing frequently updated color correction information for a color printer from a spectrophotometer in the output path of a color printer which is measuring the colors on color test patches printed on test sheets, wherein reduced wastage of paper for said printed test sheets, and reduced interruptions of normal printing, is provided by printing both banner sheet information and said color test patches on dual mode banner sheets.
As is well known in the art, it is a common practice, especially in shared user or system printers, to automatically generate and output an identifying banner sheet ahead of each individual print job being printed and outputted. Examples of banner sheets and their generation are disclosed, for example in Xerox Corp. U.S. Pat. Nos. 5,547,178 and 5,316,279, and in various commercial printer products. Accordingly, the generation, content and use of banner sheets per se need not be described in detail herein. A banner sheet may typically have automatically printed thereon by system and/or printer controller software a limited amount of printed information about that particular document or print job, such as one or more of the following text items: the print job or document name, printer user""s (document transmitter""s) name or acronym, printer code name, the host intranet system name, file name, date, the numbers of pages in that document or print job, etc.
In the present system, some or all of the banner sheets generated by the printer are also compatibly printed with color test patterns or patches and used as color test sheets for automatically generating and updating printer color control, as will be described in the example herein. Thus, there are automatically provided dual-mode color test sheets/banner sheets, in which multiple color patches of different colors are printed on otherwise blank areas of each, or selected, banner sheets.
This automatic dual mode banner sheet/color test sheet system can be implemented by relatively minor software changes well within the skill of that art at low cost and without having to otherwise modify the color printer, or interfere with or interrupt normal printing, or require any hardware changes. It can provide color test sheet printing intervals at regular timed intervals, and/or at each machine xe2x80x9ccycle-upxe2x80x9d, or as otherwise directed by the system software. It does not limit, however, the alternative or intermixed printing of conventional banner sheets without colors, or fully dedicated color test sheets which are not banner sheets.
The term xe2x80x9cbanner sheetsxe2x80x9d as used herein broadly encompasses various on-line printed cover sheets or other inter-document or inter-print-job separator sheets. Providing the subject dual use of such sheets saves both print paper and printer utilization time, and provides frequent color re-calibration opportunities, with no extra fed sheet requirements, where the printing system is one in which banner sheets are being printed at frequent intervals anyway. As noted, is quite common for shared user printers (even those with mailbox system job separators) to automatically generate and print a banner sheet immediately preceding the first page of each actual document being printed. Thus, banner sheets are being fed, printed, and fed out through the output path of a printer at frequent intervals.
Furthermore, it is common for printers, as described in the above-cited patents, to already provide automatic lateral offsetting of its banner sheets as they stack in the output tray, as compared to the other or actual document sheets, to provide print job separators, and to make the banner sheets readily separable from the actual documents. With the present dual mode sheets system, this makes separation and removal of color test sheets equally easy, in fact, accomplished at the same time by the same steps.
As indicated, with the disclosed dual mode banner sheet and color test sheets system the same banner sheets already being generated and printed in many printers may now also be used to variously print thereon the multiple color test patches for the spectrophotometer analysis by the disclosed or other output color control systems. This dual mode sheet usage system saves substantial amounts of otherwise wasted paper which would otherwise be used for non-image color test sheets which would be separated out and discarded after being outputted by the printer in addition to the banner sheets. Furthermore, this system enables frequent color re-correction inputs with no reduction in printer productivity. That is, normal document printing in a color printer does not have to be relatively frequently interrupted to print extra (non-document imaged) color test sheets to keep each color printer re-calibrated.
As discussed elsewhere herein, relatively frequent color re-calibration of a color printer is desirable, since the colors actually printed on the output can change or drift out of calibration with the intended colors for various known reasons. For example, changes in the selected or loaded print media (differences paper or plastic sheet types, materials, weights, calendering, coating, humidity, etc.), changes in the printer""s ambient conditions, changes in image developer materials, aging or wear of printer components, varying interactions of the different colors being printed, etc.
The disclosed embodiment is thus a valuable feature for a practical on-line xe2x80x9creal timexe2x80x9d color printing color calibration or correction system which regularly measures with a spectrophotometer the actual colors currently being printed on printed sheets being outputted by the printer, as compared to the intended (or selected, or xe2x80x9ctruexe2x80x9d) colors of the electronic document images being inputted to the printer for printing.
As used in the patent claims and elsewhere herein unless otherwise specifically indicated, the term xe2x80x9cspectrophotometerxe2x80x9d may encompass a spectrophotometer, colorimeter, and densitometer, as broadly defined herein. That is, the word xe2x80x9cspectrophotometerxe2x80x9d is to be given the broadest possible definition and coverage in the claims herein, consistent with the rest of the claims themselves. The definitions or uses of terms vary or differ among various scientists and engineers. However, the following is an attempt to provide some simplified clarifications relating and distinguishing the respective terms xe2x80x9cspectrophotometerxe2x80x9d, xe2x80x9ccalorimeterxe2x80x9d, and xe2x80x9cdensitometerxe2x80x9d, as they may be used in the specific context of specification examples of providing components for an on-line color printer color correction system, but not as limitations.
A typical xe2x80x9cspectrophotometerxe2x80x9d measures the reflectance of an illuminated object of interest over many light wavelengths. Typical prior spectrophotometers in this context use 16 or 32 channels measuring from 400 nm to 700 nm or so, to cover the humanly visible color spectra or wavelength range. A typical spectrophotometer gives color information in terms of measured reflectances or transmittances of light, at the different wavelengths of light, from the test surface. (This is to measure more closely to what the human eye would see as a combined image of a broad white light spectra image reflectance, but the spectrophotometer desirably provides distinct electrical signals corresponding to the different levels of reflected light from the respective different illumination wavelength ranges or channels.)
A xe2x80x9ccolorimeterxe2x80x9d normally has three illumination channels, red, green and blue. That is, generally, a xe2x80x9ccalorimeterxe2x80x9d provides its three (red, green and blue or xe2x80x9cRGBxe2x80x9d) values as read by a light sensor or detector receiving reflected light from a color test surface sequentially illuminated with red, green and blue illuminators, such as three different color LED""s or three lamps with three different color filters. It may thus be considered different from, or a limited special case of, a xe2x80x9cspectrophotometerxe2x80x9d, in that it provides output color information in the trichometric quantity known as RGB.
Trichometric quantities may be used for representing color in three coordinate space through some type of transformation. Other RGB conversions to xe2x80x9cdevice independent color spacexe2x80x9d (i.e., RGB converted to conventional L*a*b*) typically use a color conversion xe2x80x9clookup tablexe2x80x9d system in a known manner. (Examples are provided in patents cited below, and elsewhere.)
A xe2x80x9cdensitometerxe2x80x9d typically has only a single channel, and simply measures the amplitude of light reflectivity over a range of wavelengths, which may be wide or narrow. The output of the densitometer detector is programmed to give the optical density of the sample. A densitometer is basically xe2x80x9ccolor blindxe2x80x9d. For example, a cyan patch and magenta patch could have the same optical densities as seen by a densitometer, but, of course, are different colors.
A multiple LED""s reflectance spectrophotometer, as in the example of the embodiment herein, may be considered to belong to a special case of spectrophotometers. (Others, with different respective illumination sources, can be flashed Xenon lamp spectrophotometers, or QH spectrophotometers.) It is a spectrophotometer programmed to give truer reflectance values by using more than 3 channel measurements (e.g., 10 or more channel measurements), with conversion algorithms. That is in contrast to normal colorimeters, which cannot give true, human eye related, reflectance spectra measurements, because they have insufficient measurements for that (only 3 measurements).
As noted, the type of spectrophotometer in the disclosed embodiment is a spectrophotometer especially suitable for being mounted in the printed sheets output path of a color printer to optically evaluate the output sheets as they move past the spectrophotometer. In particular, to measure a limited number of color test patch samples printed by the printer on actual printed sheet output of the printer during regular or selected printer operation intervals (between normal printing runs or print jobs). These color test sheet printing intervals may be at regular timed intervals, and/or at each machine xe2x80x9ccycle-upxe2x80x9d, or as otherwise directed by the system software.
A low cost and relatively simple yet easily calibrated spectrophotometer, as disclosed in the example below, is highly desirable for such a xe2x80x9ccolorimetryxe2x80x9d function for such an on-line color correction system, since a dedicated spectrophotometer must be provided for each printer. A patent of background interest as to using a type of spectrophotometer at the printed sheets output of a color printer is Xerox Corp. U.S. Pat. No. 5,748,221 issued May 5, 1998 to Vittorio Castelli, et al, filed Nov. 1, 1995 (D/95398).
Also noted are pending Xerox Corp. U.S. application Ser. No. 09/083,202, filed May 22, 1998, now issued as U.S. Pat. No. 6,236,474 on May 22, 2001 by Mark A. Scheuer, et al., entitledxe2x80x9cDevice Independent Color Controller and Method,xe2x80x9d U.S. application Ser. No. 09/083,203, filed May 22, 1998 by Lingappa K. Mestha, entitled xe2x80x9cDynamic Device independent Image,xe2x80x9d now issued as U.S. Pat. No. 6,157,469 on Dec. 5, 2000, U.S. application Ser. No. 09/232,465, filed Jan. 19, 1999, now issued as U.S. Pat. No. 6,344,902 on Feb. 5, 2002 by Martin E. Banton, et al., entitled xe2x80x9cApparatus and Method for Using Feedback and Feedforward in the Generation of Presentation Images In A Distributed Digital Image Processing System,xe2x80x9d and U.S. application Ser. No. 09/221,996, filed Dec. 29, 1998 by Lingappa K. Mestha, et al., entitled xe2x80x9cColor Adjustment Apparatus and Method,xe2x80x9d.
Another example of a test sheet with color test patches automatically generated by a color printer, for operator use, is shown in Xerox Corp. U.S. Pat. No. 5,604,567 issued Feb. 18, 1997 to Peter H. Dundas, et al.
Color correction and/or color control systems should not be confused with color registration systems or sensors. Those systems are for insuring that colors are correctly printed accurately superposed and/or accurately adjacent to one another, such as by providing positional information for shifting the position of respective color images being printed.
Other background patents which have been cited as to color control or correction systems for printers include Xerox Corp. U.S. Pat. No. 5,963,244 issued Oct. 5, 1999 to L. K. Mestha, et al entitled xe2x80x9cOptimal Reconstruction of Tone Reproduction Curvexe2x80x9d (using a lookup table and densitometer readings of photoreceptor sample color test patches to control various color printer parameters); and U.S. Pat. No. 5,581,376, issued December 1996 to Harrington; U.S. Pat. No. 5,528,386 issued Jun. 18, 1996 to Rolleston et al.; U.S. Pat. No. 4,275,413 issued Jun. 23, 1981 to Sakamoto et al.; U.S. Pat. No. 4,500,919 issued Feb. 19, 1985 to Schreiber; U.S. Pat. No. 5,416,613 issued May 16, 1995 to Rolleston et al.; U.S. Pat. No. 5,508,826 issued Apr. 16, 1996 to Lloyd et al.; U.S. Pat. No. 5,471,324 issued Nov. 28, 1995 to Rolleston; U.S. Pat. No. 5,491,568 issued Feb. 13, 1996 to Wan; U.S. Pat. No. 5,539,522 issued Jul. 23, 1996 to Yoshida; U.S. Pat. No. 5,483,360 issued Jan. 9, 1996 to Rolleston et al.; U.S. Pat. No. 5,594,557 issued January 1997 to Rolleston et al.; U.S. Pat. No. 2,790,844 issued April 1957 to Neugebauer; U.S. Pat. No. 4,500,919 issued February 1985 to Schreiber; U.S. Pat. No. 5,491,568 issued Feb. 13, 1996 to Wan; U.S. Pat. No. 5,481,380 to Bestmann issued Jan. 2, 1996; U.S. Pat. No. 5,664,072 issued Sep. 2, 1997 to Ueda et al.; and U.S. Pat. No. 5,544,258 issued Aug. 6, 1996 to Levien.
By way of further background on the subject of technology for automatic color correction for color printers or other reproduction apparatus, especially such systems utilizing feedback signals from a colorimeter or spectrophotometer (as noted, those terms may be used interchangeably herein), and/or automatically measuring the actually printed colors of test patches on printed copy sheets as they are being fed through the output path the printer, there is noted the following: the above-cited Xerox Corporation U.S. Pat. No. 5,748,221 filed Nov. 1, 1995 and issued May 5, 1998 to V. Castelli, et al; entitled xe2x80x9cApparatus for Colorimetry, Gloss and Registration Feedback in a Color Printing Machinexe2x80x9d, (noting especially the output path test print calorimeter detector details); the above-cited Apple Computer, Inc. U.S. Pat. No. 5,612,902, issued Mar. 18, 1997 to Michael Stokes; Xerox Corporation U.S. Pat. No. 5,510,896 issued Apr. 23, 1996 to Walter Wafler, filed Jun. 18, 1993 (see especially Col. 8 re color calibration from information from a scanned color test copy sheet as compared to original color image information); and Xerox Corporation U.S. Pat. No. 5,884,118 issued Mar. 16, 1999 to Mantell and L. K. Mestha, et al, entitled xe2x80x9cPrinter Having Print Output Linked to Scanner Input for Automated Image Quality Adjustmentxe2x80x9d (note especially Col. 6 lines 45-49).
U.S. Patents of interest to color correction in general, but which may be useful with, or provide background information for, the above or other systems, includes the above-cited Xerox Corporation U.S. Pat. No. 5,594,557, filed Oct. 3, 1994 and issued Jan. 14, 1997 to R. J. Rolleston et al., entitled xe2x80x9cColor Printer Calibration Correcting for Local Printer Non-Linearitiesxe2x80x9d; Seiko Epson Corp. U.S. Pat. No. 5,809,213, provisionally filed Feb. 23, 1996 and issued Sep. 15, 1998 to A. K. Bhattacharjya re reduced color measurement samples; and Splash Technology, Inc. U.S. Pat. No. 5,760,913 filed Feb. 12, 1996 and issued Jun. 2, 1998 to Richard A. Falk in which a calibration image is scanned using a scanner coupled to the printing system with a personal computer.
Also noted are pending Xerox Corp. U.S. applications Ser. No. 09/083,202 filed May 22, 1998 by Mark A. Scheuer, et al., entitled xe2x80x9cDevice Independent Color Controller and Methodxe2x80x9d Ser. No. 09/232,465, filed Jan. 19, 1999 by Martin E. Banton, et al., entitled xe2x80x9cApparatus and Method for Using Feedback and Feedforward in the Generation of Presentation Images In A Distributed Digital Image Processing Systemxe2x80x9d, and Ser. No. 09/221,996, filed Dec. 29, 1998 by Lingappa K. Mestha, et al., entitled xe2x80x9cColor Adjustment Apparatus and Methodxe2x80x9d, and U.S. Pat. No. 6,157,409.
As further well-known background for the reader on the subject of difficulties in color correction of printers in general, computers and other electronic equipment generating and inputting color images or documents typically generate three-dimensional or RGB (red, green, blue) color signals. Many printers, however, can receive four-dimensional or CMYK (cyan, magenta, yellow, and black) signals as input, and/or can print with four such print colors (although the printed images can be measured as corresponding RGB values). A look-up table is commonly provided to convert each digital RGB color signal value to a corresponding digital CMYK value before or after being received by the printer. Another difficulty is that a theoretical printer which had ideal toner, ink or dye printing materials colors and printing behavior would have a one-to-one correspondence of cyan-to-red, magenta-to-green, and yellow-to-blue. This would mean that when printed, the cyan ink would only absorb red light, the magenta ink would only absorb green light, and the yellow ink would only absorb blue light. However, real-world printers inherently have non-ideal printing materials colors and behaviors, and therefore have complex non-linear calorimetric responses. Also, interactions between the cyan, magenta, and yellow imaging materials exist, especially on the printed output, which result in unwanted or unintended absorptions of colors. Even after a printer is initially calibrated, such that one or a range of input digital CMYK values produce the proper color(s), the full spectrum of CMYK values and printed colors is not accurate. In other words, the colors asked or directed to be printed are not the same as the actual colors printed.
This discrepancy arises in part because the relationship between the digital input values that drive the printer and the resulting colorimetric response is a complex non-linear function. Labeling the response, or other values, as xe2x80x9ccalorimetricxe2x80x9d can indicate that the response or value has been measured by such an instrument. Adequately modeling the colorimetric response of a printer to achieve linearity across the entire available spectrum requires many parameters. Typically, a color correction look-up table is built which approximates the mapping between RGB colorimetric space and CMYK values, as taught in various of the above-cited references. Each RGB coordinate may be typically represented by an 8-bit red value, an 8-bit green value, and an 8-bit blue value. Although those RGB coordinates are capable of addressing a look-up table having 2563 locations, measuring and storing 2563 values is expensive. The look-up table is thus typically partitioned into a smaller size such as 16xc3x9716xc3x9716 (4096) table locations, each of which stores a four-dimensional CMYK value. Other CMYK values may then be found by interpolating the known CMYK values using an interpolation process, for example, trilinear or tetrahedral interpolation.
The color correction look-up table may be built by sending a set of CMYK digital values to the printer, measuring the colorimetric RGB values of the resulting color patches outputted by the printer, and generating the look-up table from the difference between the inputted values and the measured outputted values. More specifically, the color correction look-up table corrects for non-linearities, printing parameter variations, and unwanted absorptions of inks, so that the printer will print the true corresponding color.
After the color correction table is generated, the actual printer response tends to drift over time. To correct for the drift, the system is adjusted or recalibrated periodically. Recalibrating the color correction table involves periodically printing and remeasuring a set of test color patches which are then compared to an original set of color patches by calibration software. Remeasuring, however, has heretofore more typically been performed by a scanner or other measuring device which is remote from the printer being recalibrated. In that case, an operator must manually reconfigure the scanner and calibration software to properly recognize and measure the test color patches. This assumes that the operator can properly identify the test color patches being tested in accordance with the original printer and its test pattern properties. Furthermore, once a color correction table is generated, it must be associated with the correct printer, otherwise, a different printer will be recalibrated with an incorrect correction table. The above-cited references on automatic, on-line, color correction note the important advantages of being able to provide direct output color measurements for each printer.
The present invention thus also provides for a new and improved system and method of assisting in the frequent rer-calibrating of a color printer and/or refining color correction tables which overcomes various above-referenced and other problems, although not limited thereto.
For maintaining high quality color reprographics, it is highly advantageous to frequently monitor system calorimetric performance on-line through the use of an integrated spectrophotometer. That is, to have the printing device frequently automatically generate calibration prints on otherwise normally printed sheets with color patches based on digital test pattern generations, and to have an on-line spectrophotometer in the printer output read those moving printed color test patches to provide printed output color measurement signals. This requires fairly frequent test sheet printing and a spectrophotometer capable of effectively operating in that environment and under those conditions to read those test sheets accurately, which are not typical for conventional laboratory spectrophotometers. That is provided by the spectrophotometer disclosed herein, but the subject system is not limited thereto.
A specific feature of the specific embodiment disclosed herein is to provide in a color printer for printing multiple print jobs comprising sequentially printed color sheets, said color printer having a banner sheet printihg system for automatically printing banner sheets preceding respective said print jobs, said banner sheets having printed thereon identifying information relating to said print jobs, and said color printer having an output path for outputting said printed color sheets in a process direction, the improvement in said color printer comprising: a printed colors measurement system, said printed colors measurement system including a spectrophotometer mounted in said output path and a color test prints generation system for periodically printing multiple different color test patches on special said printed color sheets being printed and outputted through said output path as printed color test sheets, said spectrophotometer being adapted to sense said different colors printed on said color test patches on said printed color test sheets in said output path, wherein at least a plurality of said printed color test sheets printed by said color printer with said multiple different color test patches are dual mode sheets comprising said banner sheets printed by said banner sheet printing system with said identifying information printed thereon relating to said print jobs wherein said banner sheet printing system and said color test prints generation system are coordinated so that said banner sheet printed identifying information and said multiple different color test patches are printed in different areas of said dual mode sheets so as to not overprint one another.
Further specific features disclosed herein, individually or in combination, include those wherein said multiple different color test patches are printed in a limited area of said dual mode sheets extending across said dual mode sheet in said process direction and said banner sheet printed identifying information is printed on said dual mode sheets outside of said limited area; and/or wherein said color test prints generation system is further adapted to generate a dual mode color test print and banner sheet printed with at least one color test patch corresponding to a color to be printed in said print job for which said dual mode sheet is said banner sheet; and/or a method of color printing in a color printer which automatically prints and outputs printed sheets through an output path in a process direction, including printed sheets which are banner sheets printed with banner sheet information relating to a subsequently printed print job, which color printer is provided with a color measurement system for measuring printed colors on printed sheets in said output path, comprising: automatically printing an array of multiple color test patches for said color measurement system on a multiplicity of said automatically printed banner sheets, said array of multiple color test patches being printed in an area of said banner sheet extending across said banner sheet in said process direction, and said printed banner sheet information being printed on said banner sheet outside of said area of said banner sheet in which said array of multiple colored test patches is printed; and/or wherein at least part of said subsequently printed print job is to be printed with at least one specific color, further comprising printing on said banner sheet for said print job at least one color test patch corresponding to said specific color to be printed in said subsequently printed print job.
The disclosed system may be connected, operated and controlled by appropriate operation of conventional control systems. It is well known and preferable to program and execute various control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software and computer arts. Alternatively, the disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
In the description herein the term xe2x80x9csheetxe2x80x9d refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopyxe2x80x9d, or called a xe2x80x9chardcopyxe2x80x9d As will be noted, printed sheets may be referred to as xe2x80x9coutputxe2x80x9d. A xe2x80x9cprint jobxe2x80x9d is normally a set of related printed sheets, usually one or more collated copy sets copied from a one or more original document sheets or electronic document page images, from a particular user, or otherwise related.
As to specific components of the subject apparatus, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described here.
Various of the above-mentioned and further features and advantages will be apparent from the specific apparatus and its operation described in the example below, and the claims. Thus, the present invention will be better understood from this description of a specific embodiment, including the drawing figures (approximately to scale, except for schematics).